By Heidi Vogt and Timothy Puko 

WASHINGTON -- The Commerce Department has opened an investigation into whether uranium imports threaten national security, a move that could pave the way for tariffs on foreign producers of the radioactive material that fuels nuclear power plants.

Uranium is used in commercial reactors that power a significant portion of the country's electrical grid, as well as in Navy submarines and aircraft carriers. Tariffs could be imposed if the investigation finds that the use of imported uranium could make the U.S. too dependent on foreign countries for an essential material.

U.S. uranium production has dropped to 5% of what's required for the military and the country's nuclear infrastructure from 49% in 1987, according to a statement from Commerce Secretary Wilbur Ross Wednesday. He promised a "thorough, fair and transparent review."

Canada is the largest source of imported uranium for civilian power plants, followed by Australia, Russia, Kazakhstan and Uzbekistan, according to the U.S. Energy Information Administration.

The Commerce Department is using a trade law called Section 232, which officials say gives them wide authority to define national security in economic terms and block imports to achieve their goals.

They already used Section 232 to apply new tariffs on steel and aluminum imports from Canada, Mexico and the European Union, and Mr. Trump's threat of 20% auto tariffs are tied to a Commerce Department study of whether car and auto imports can be considered a national-security threat.

Those moves are facing a constitutional challenge from a group representing users of imported steel. They argue the decades-old law improperly delegates trade powers to the executive branch from the legislative branch in violation of the Constitution.

The Commerce Department opened the uranium investigation after a petition from two major U.S. uranium mining companies -- UR-Energy Inc. and Energy Fuels Inc. The two companies have laid off more than half their workforce in the past two years and both are operating at less than 14% of their capacity, according to the statement.

The Commerce Department said uranium powers nuclear reactors that provide 20% of the electricity in the country's electrical grid.

The Nuclear Energy Institute -- a trade association -- put out a statement ahead of the announcement saying it supports efforts to protect the uranium mining industry as long as it doesn't increase the financial issues of the struggling nuclear energy sector.

NEI President and Chief Executive Maria Korsnick said in the statement issued Monday that the industry is "facing significant economic stress."

"The loss of domestic mining would have a significant detrimental impact on U.S. strategic interests," she said. "However, any action taken should not impose onerous financial burdens on companies operating the U.S. nuclear fleet," she said.

Write to Heidi Vogt at heidi.vogt@wsj.com and Timothy Puko at tim.puko@wsj.com

(END) Dow Jones Newswires

July 18, 2018 13:31 ET (17:31 GMT)